I don't know about ATHA, but I have a weakness for Yankee push drills, originally made by North Bros., which was purchased by Stanley in 1946. I've seen three labels on the drills:
1. "North Bros., Philadelphia, PA" (my favorite - my bride's a Philly native)
2. "North Bros., a division of Stanley"
3. "Stanley"
I assume that this is the chronological development of the labels, with the first label indicating tools made before the Stanley acquisition, and the second and third showing the absorption over time of the North Bros. products into the Stanley line.
Stanley, in my observation, was always pretty quick to plant its corporate flag on its products after buying yet another company. When Microsoft started dealing with its competition by buying the companies, back in the 1970s and 80s, people acted like it was a new idea; Stanley had been doing it for over a century by then.
Again, I have no knowledge of ATHA tools; but, in the absence of other information, I'd lean toward this being a pre-Stanley tool.
I do like the Maydole pattern hammers, like yours, with just a smooth taper from eye to striking face; I've purchased a couple of rusty ones with funky handles, just to have that shape, even though I've got plenty of claw hammers already (and was delighted to find one was an actual Maydole hammer!).
